I. Field of the Invention:
This invention relates generally to a cutting tool, and more particularly to a so-called "utility knife" of the type incorporating a replaceable blade supported in a gripping handle and wherein the length of the blade extending beyond the end of the handle can be infinitely adjusted and then locked in a preset position.
II. Discussion of the Prior Art:
Various forms of utility knives are known in the prior art. They generally comprise a blade which can be clamped or gripped in a handle and used for cutting a variety of items including carpeting, cardboard, vinyl and cloth fabircs, trimming wallpaper, etc. When the blade becomes dulled by such use, it is taken out, discarded and replaced with a new blade. One well-known utility knife is that manufactured by the Stanley Tool Co. and it comprises a flat, trapezoidally-shaped blade having a pattern of notches in one side edge thereof, the blade being contained within a two-piece handle, the pieces of the handle being held together by a suitable fastener and the blade being locked against movement by virtue of a suitably positioned projection which engages the notches on the blade.
Another form of utility knife is disclosed in the Anderson et al U.S. Pat. No. 4,109,380 which has been assigned to the assignee of the present invention. That knife comprises a generally rectangular blade whose two opposed side edges are each honed to a fine cutting edge and which does not rely upon notches formed in the blade to hold it fixed relative to its handle. Instead, the slit where the blade exits the end edge of the blade holder is provided with a predetermined taper at its edges and the length of the slit is slightly greater than the width of the blade. Hence, when a cutting force is applied to the blade by pressing it against the item to be cut, the blade cocks in its handle and the cutting edge becomes wedged in the tapered end of the slit formed in the end of the handle. This wedging action prevents longitudinal movement of the blade relative to the handle.
Another utility knife now on the market is manufactured by Kimkead and sold under its trademark "KINYRIM". This utility knife also includes a blade holder in the form of a handle having a goose-neck head quite similar in construction to the embodiment shown in FIG. 9 of the aforereferenced Anderson patent. In this arrangement, a blade having a longitudinally extending slot fits between the separable halves of the blade holder and a screw passes through one side of the knife handle, through the slot in the blade and into a threaded bore formed in the other handle half. By tightening this screw, a clamping force is applied to the blade. Slotted blades of the type described do not stand up as well in use especially when significant pressure must be applied to the item being cut. The longitudinal slot necessarily weakens the blade and breakage often occurs.